1. Field of the Invention
The present invention relates to a three way valve assembly with a pressure compensating valve, and the pressure compensating valve serves to hold an oil pressure within an actuating oil chamber in a hydraulic apparatus at a predetermined pressure by releasing an abnormal pressure raised at a slow speed when the oil pressure within the actuating oil chamber is abnormally increased at the slow speed by a thermal expansion of the pressurized oil and so on.
2. Description of the Prior Art
As such a three way valve with a pressure compensating valve, has been known the one disclosed in the Japanese Utility Model Laid Open Publication No. 1984-68801 previously proposed by the inventor of the present invention.
As shown in FIG. 9, a basic construction of the prior art is as follows.
A three way valve assembly 201 with a pressure compensating valve is provided with a three way valve 202, a pressure compensating valve 203, left and right paired end plates 204, 205 and assembly bolts 206, 207, having said three way valve 202 and said pressure compensating valve 203 located between the left and right end plates 204, 205 and having the left and right end plates 204, 205 tightened by means of said assembly bolts 206, 207 toward the central side from left and right sides.
The three way valve 202 is provided with a first housing 210, a directional changeover valve member 211 and a directional changeover manipulation means 212.
Within the first housing 210, a pressure port P, a work port A, a return port R and an abnormal pressure relief port M are communicated to a valve chamber 215, the directional changeover valve member 211 is inserted into the valve chamber 215, and the directional changeover valve member 211 is adapted to be manipulated by the directional changeover manipulation means 212 so as to be changed over to a pressure supply position X and to a pressure discharge position.
Under a pressure supply condition where the directional changeover valve member 211 is located at the pressure supply position X, the return port R is closed and a pressurized oil within the pressure port P is supplied to the work port A through the valve chamber 215, and to the contrary under a pressure discharge condition where the directional changeover valve member 211 is located at the pressure discharge position, the pressure port P is closed and a pressurized oil within the work port A is discharged to the return port R through the valve chamber 215.
The pressure port P and the return port R are opened in the left and the right end surfaces 210a, 210b of the first housing 210, and to the contrary, said work port A is opened in a portion of an upper, lower, front or back external surrounding surface of the first housing 210.
The pressure compensating valve 203 is constructed by communicating a pressure discharge outlet port 260 to a pressure inlet port 258 through a throttling passage 259a and a relief valve chamber 260 within a second housing 257, a relief valve member 263 is inserted into the relief valve chamber 260, the pressure inlet port 258 is communicated to the work port A of the three way valve 202, and the pressure discharge outlet port 261 is communicated to the return port R of the three way valve 2.
A pressure supply port S and a pressure discharge port T are opened in the end plates 204, 205, the pressure supply port S is communicated to the pressure port P of the three way valve 202, and the pressure discharge port T is communicated to the return port R of the three way valve 202.
In the above-mentioned basic construction, a construction for mounting the three way valve 202 and the pressure compensating valve 203 between both end plates 204, 205 is conventionally as follows.
That is, as shown in FIG. 9, the second housing 257 of the pressure compensating valve 203 is kept at its left end surface in contact with the right end surface 210b of the first housing 210 of the three way valve 202 so that both the valves 202, 203 are held and fixedly secured between the left and the right end plates 204, 205 by means of the assembly bolts 206, 207. Further, between the contact surfaces of both the housings 210, 257, the pressure port P of the three way valve 202 and the pressure supply inlet port 121 of the pressure compensating valve 203, the abnormal pressure relief port M and the pressure inlet port 258, and also the return port R and the pressure discharge outlet port 261 are oil-tightly intercommunicated through O-rings 122, 123, 124 respectively.
There are, however, the following problems associated with the above-mentioned prior art.
(a) An installation plane area for the three way valve assembly 201 is large. PA0 (b) A flow characteristic of the three way valve 202 is low. PA0 (c) A necessary strength of the assembly bolts 206, 207 are large. PA0 (d) An oil leakage is apt to be caused between the contact surfaces of both the housings 210, 257. PA0 (e) It is troublesome to additionally assemble the pressure compensating valve 203. PA0 (a) An installation plane area for the three way valve becomes smaller. PA0 (b) A flow characteristic of the three way valve is improved. PA0 (c) A necessary strength of the assembly bolt can be made smaller. PA0 (d) An oil leakage between the contact surfaces of the housing can be prevented. PA0 (e) It is easy to additionally install the pressure compensating valve.
Since the three way valve assembly 201 has the three way valve 202 and the pressure compensating valve 203 assembled left and right in a side by side arrangement, the length thereof in the left and right direction becomes large and the installation plane area is large.
Since the pressure supply inlet port 121 is interposed in the second housing 257 of the pressure compensating valve 203 between the pressure supply port S and the pressure port P, a passage resistance on the pressure supply side of the three way valve 202 is large. In addition thereto, the pressure discharge outlet port 261 of the pressure compensating valve 203 is interposed between the pressure discharge port T and the return port R, the passage resistance on the pressure discharge side of the three way valve 202 is large. In that way, since the three way valve 202 is large in passage resistance both on the pressure supply side and on the pressure discharge side, the flow characteristic can't help becoming low.
At the time of pressure supply of the three way valve 202, since an oil pressure acts also on the sealing surfaces of two O-rings 122, 123 between the contact surfaces of both the housings 210, 257 so as to separate both housings 210, 257 apart, the necessary strength of the assembly bolts 206, 207 become larger by the portion corresponding to an installation of the O-rings 122, 123.
Since the assembly bolts 206, 207 can't become long in length due to the passing through both the housings 210, 257, an elongation thereof gets large at the time of pressure supply. Therefore, the O-rings 122, 123 are squeezed out between both the housings 210, 257 and an oil leakage is apt to be caused there.
In the case that the pressure compensating valve 203 is newly assembled to the already installed three way valve 202 for providing the three way valve assembly with the pressure compensating valve, since it is necessary to additionally bore bolt holes for the assembly bolts 206, 207 in the second housing 257 of the pressure compensating valve 203, it is troublesome to perform such additional work for the pressure compensating valve 203.
By the way, as shown in FIG. 10, in the case that a multiplicate three way valve assembly is constructed by arranging a plurality of three way valves 202 and pressure compensating valves 203 side by side in the left and right direction, since the length in the left and right direction becomes longer, the aforementioned problems appear as a remarkable evil.